1. Field
Embodiments of the present invention generally relate to semiconductor processing equipment and more particularly, to methods and apparatus for calibration of mass flow controllers.
2. Description of the Related Art
Continued reduction in size of semiconductor devices is dependent upon more precise control of, for instance, the flow rate of process gases delivered to a semiconductor process chamber in which such semiconductor devices are processed. Typically, the process gases are provided utilizing a mass flow controller for each process gas being delivered to the chamber.
To maintain precise control, the mass flow controllers must provide an accurate and repeatable operation. Therefore, the mass flow controllers are periodically calibrated, for example, every few weeks. Typically, a calibration process may involve individually comparing the flow rate from each mass flow controller to that of a standard mass flow controller (e.g., a mass flow controller known to be calibrated accurately) at a known pressure and temperature. Unfortunately, the calibration process can only be performed to an uncertainty of about 5% for each mass flow controller, which may be too imprecise for future processing. In addition, the calibration of the mass flow controllers drift over time, leading to process variation. Furthermore, the standard mass flow controller also drifts over time, which can further result in inaccurate calibrations.
Accordingly, there is a need in the art for methods and apparatus to calibrate mass flow controller to greater certainty.